Are you attempting to run builds directly against the repository at https://github.com/google/googlesignin-ios, a branch on that repo, or have you created your own fork of their repo? Also, are you able to attach the .xcresult file?

+1 to the DTS Engineer's recommendation to file a bug report. Also: Have you tried creating a new Xcode Cloud workflow which just performs a Build action without attempting to run any tests? I'd be curious if that would succeed and how long it would take.